We have initially developed the first multitarget-ribozymes in the context of an antiviral strategy against the human immunodeficiency virus (HIV-1). Their antiviral activity was very effective and specific to justify an entire project dedicated to the development and application of these catalytic RNAs not only against viruses but also against cellular RNAs. We had previously determined that multitarget-ribozymes can be synthesized which catalytically cleave target RNA very efficiently at multiple sites in vitro, functioning simultaneously like several restriction enzymes for RNA. This multiple sequence specificity was also demonstrated by us in vivo after HIV-1 infections. Most importantly, we had found that at the same molar ratio, multitarget-ribozymes are much more effective in RNA cleavage than single ribozymes. In addition, multitarget-ribozymes seemed to retain most of their activity even when they are buried within a large RNA transcript. These features could be very attractive, for example, in protein replacement experiments or even in therapies. These results also suggested that multitarget-ribozymes could also be used to eliminate the expression of genes in transgenic animals without requiring homologous recombination after appropriate localized delivery to differentiated cells in vivo possibly through viral vectors. Towards these goals, we need to understand the precise mechanism of ribozyme action, its intracellular site of action, how efficient target sites can be selected, etc. We anticipate that these studies will lead us to new analytical tools for the study of cell function and possible treatment of cellular dysfunctions of the central nervous system as well as other organs. This project has only been initiated recently and, although we have assembled several DNAs encoding mutated multitarget- ribozymes, we do not have a definite answer as yet in which cellular compartment ribozymes are active and whether multitarget-ribozymes can in part also function as antisense molecules.